Cerebellum and Motor System Overview

Cerebellum, Basal Nuclei & Extrapyramidal System

• Learning Outcomes: Describe cerebellum structure, mechanisms of balance and coordination, cerebellar disease relating to region anatomy, identify basal nuclei parts, and relate anatomy to clinical problems (e.g., Parkinson's, Huntington's diseases).

General Organization of Motor System

• Diagram: Shows the motor system pathway, from cerebral cortex, through the brainstem, thalamus, basal ganglia, and cerebellum, to the spinal cord and muscles. Includes corticospinal tracts, corticobulbar projection, extrapyramidal tracts, afferent neurons, and motor neurons.

Cerebellar Position in Cranium

• Location: Cerebellum is in the posterior cranial fossa.
• Covered by: Tentorium cerebelli
• Structures: Diagram highlights various grooves and landmarks including the groove for inferior petrosal sinus, superior border of petrous part of temporal bone, groove for sigmoid sinus, jugular tubercle, internal acoustic meatus, jugular foramen, hypoglossal canal, groove for transverse sinus, tentorial notch, foramen magnum, internal occipital crest, internal occipital protuberance, falx cerebri, infundibulum, tentorium cerebelli, and falx cerebelli.

Functional Connections of Cerebellum

• Connections: Connected to other parts of the nervous system through peduncles.
• Superior peduncle: Connects to the midbrain.
• Middle peduncle: Connects to the pons.
• Inferior peduncle: Connects to the medulla oblongata.

Cerebellum

• Structure: Two hemispheres and a vermis (midline structure) are visible in a diagram.
• Lobes: Anterior, Posterior/Middle, and Flocculonodular lobes are labeled.

Divisions of Cerebellum - Multiple Ways

• Anatomical Divisions: Anterior, Posterior/Middle, and Flocculonodular.
• Functional Divisions: Vestibulocerebellum, Spinocerebellum, and Cerebrocerebellum.
• Evolutionary Divisions: Archicerebellum, Paleocerebellum, and Neocerebellum.

Functional Divisions

• FN Lobe (Vestibulocerebellum): Deep cerebellar nuclei—Fastigial, interconnected with vestibular nuclei, posture, balance, and eye movements. Lesion causes flocculonodular lobe syndrome including nystagmus, balance loss, and gait disturbance.

• Spinocerebellum: Deep cerebellar nuclei—Globose & Emboliform, input from vermis & paravermis from spinal cord, maintains posture & muscle tone. Lesion cases anterior lobe syndrome with nystagmus, balance loss, and gait disturbance.

• Cerebrocerebellum: Deep cerebellar nuclei—Dentate, principle input from cortex to lateral hemisphere, concerned with coordination, planning, and execution of movements, feedback to motor cortex to correct movement errors. Lesion cause posterior lobe syndrome including incoordination, unsteady gait, and issues with motor skills.

Summary of Major Efferents from Cerebellum

• Origin: Flocculonodular lobe via Fastigial nucleus, Inferior peduncle.
• Pathway: Projects to vestibular nucleus and reticular formation, Inferior peduncle.
• Function: Coordination of posture, bilateral proximal and truncal muscle tone, and eye movements, coordination of posture, proximal and truncal muscle tone and eye movements.
• Disorder: Disturbed gait (wide ataxic gait), balance loss, nystagmus, no ataxia in limbs, truncal limb ataxia ipsilateral to lesion.

Deep Cerebellar Nuclei

• Location: Within the white matter.
• Nuclei (Medial to Lateral): Fastigial nucleus (archicerebellum, balance and equilibrium), Interposed nuclei (paleocerebellum, walking and arm movements e.g., Globose and Emboliform), and Dentate nucleus (neocerebellum, higher-order motor skills).
• Function: Receive inputs from incoming and outgoing cerebellum neurons, modulate/regulate cerebellum's influence on the nervous system.

Blood Supply to Cerebellum

• Arteries: Superior cerebellar artery (SCA), Anterior inferior cerebellar artery (AICA), and Posterior inferior cerebellar artery (PICA).
• Vascular Territories: SCA, AICA, and PICA supply different parts of the cerebellum.
• Vascular Problems: SCA and PICA are common problems, mostly SCA infarcts presenting with pure cerebellar signs. PICA and AICA have sensory and motor deficits.

Lesions

• Midline/Vermis Lesions: Vestibulocerebellum/Spinocerebellum - Cause nystagmus, loss of balance and gait disturbance.
• Lateral Lesions: Cerebrocerebellum - Cause problems in coordination, unsteady gait, no sensory deficit or weakness. Lesions are ipsilateral.
• Bilateral Lesions: Cause lack of coordination, intention tremor, unsteady gait.

Key Features of Cerebellar Lesions

• Ataxia: Incoordination of movements.
• Intention Tremor: Tremor increases as the task nears completion.
• Dysmetria: Inability to accurately reach a target.
• Dysdiadochokinesia: Difficulty performing rapid alternating movements.
• Nystagmus: Oscillatory eye movements.
• Hypotonia: Decreased muscle tone.
• Pendular Knee Jerks: Abnormal "pendulum"-like knee reflexes.

Divisions of Cerebellum: Summary

• Summary table listing anatomical, phylogenetic, functional classifications and deep nuclei associated with each region.

Cerebellar Tonsil and Foramen Magnum Relation

• Tonsil position.
• Increased intracranial pressure pushes cerebellar tonsil through the foramen magnum compressing medulla.

Basal Ganglia: Major Components

• Structure: Islands of gray matter embedded in subcortical white matter.
• Components: Caudate, Putamen, Globus Pallidus, Subthalamic nucleus, and Substantia nigra.

Basal Ganglia: Major Components (continued)

• Structure and Function: Continued description of basal nuclei components and their locations

Basal Ganglia: Major Components (continued)

• Structure and Function: Further description of basal nuclei components, their location and relationships to each other including the insula

Coronal Section

• Structure: Shows a sagittal section of the brain and identifies the major parts of the basal ganglia including the head of the caudate nucleus, putamen, globus pallidus, internal capsule and thalamus. 

Transverse Section

• Structure: Shows a transverse section of the brain, identifies the major parts of the basal ganglia including the head of the caudate nucleus, putamen, globus pallidus, internal capsule and thalamus

Neostriatum (Caudate + Putamen)

• Input Station: Receiving station for input from the brain.
• Inputs: Cerebral Cortex ("Corticostriate Pathway"), Substantia Nigra ("Nigrostriate Pathway"), Thalamus (Centromedian Nucleus)

Globus Pallidus and Substantia Nigra Reticulata

• Output Stations: major output stations for basal ganglia, project to the thalamus
• Outputs: "Pallidothalamic" and "Nigrothalamic" pathways.

Basal Nuclei Connections

• Key Points: 2 separate pathways, direct (allows movement), indirect (inhibits unwanted movement).
• Inputs: Mainly from cortex, thalamus, substantia nigra (pars compacta).
• Outputs: Globus pallidus (internal segment), pars reticulata of substantia nigra, to cortex and UMNs (via thalamus ventral anterior & ventral lateral nucleus).

Parkinson's Disease

• Cause: Loss of dopaminergic neurons in substantia nigra (pars compacta/nigrostriatal pathway).
• Symptoms: Tremors (resting tremor), rigidity, akinesia (difficulty initiating movement), postural and gait disturbances (e.g., slow, stooped posture, shuffling gait), festinant gait (as though running).

Huntington's Disease (HD)

• Cause: Degenerative lesions in the caudate nucleus, neuronal loss in striatum and cortex (frontal, parietal).
• Symptoms: Progressive dementia, chorea (brief, sudden, purposeless jerks).

Basal Nuclei Pathologies

• Parkinson's and Huntington's diseases. Descriptions of the pathology of each.
• Hemiballismus: Flailing, ballistic, undesired movements of the limbs, damage in contralateral subthalamic nucleus.

References and Practice Questions